The present invention relates to a technology used in an image capturing apparatus which enables to capture the image of a physical object and display the captured image for displaying a graded scale to be used for indicating the dimension of the physical object so as to be displayed as an over layer onto the captured image.
In recent years, the image capturing apparatus to capture the image of the physical object under observation and to display the captured image in real time on the displaying part such as Liquid Crystal Display and organic/inorganic EL (electro-Luminescence) display has been widespread, for example, including endoscope, digital still camera and digital video camera. Such image capturing apparatus complete s imaging of the reflected light from the physical object as the object image on the imaging sensor such as CCD and CMOS by using the image capturing optical part comprising lens system, and then captures the completed object image.
The object image completed onto the imaging sensor using the image capturing optical part generally has a distortion in comparison with the actual physical object due to distortion aberration at the image capturing optical part. An example of distortion will be described by referring to FIG. 11 for better understanding.
FIG. 11 shows an illustration describing the distortion in the object image due to distortion aberration at the image capturing optical system. FIG. 11 (a) illustrates the actual physical object. FIG. 11 (b) illustrates the completed imaging of the physical object shown in FIG. 11 (a) by using the image capturing optical part having a barrel-shaped distortion aberration characteristic. As found in those figures, as the object image completed by the image capturing optical part has a distortion in comparison with the actual physical object, the captured image captured by the image capturing apparatus also becomes a distorted image in comparison with the actual physical object.
The barrel-shaped distortion as shown in FIG. 11 (b) is found in case that a wide-angle lens system is used as the image capturing optical part, and is also found to be significant in case that a wide-angle lens system is used for capturing the image at short range. As the wide-angle lens system has such a characteristic that the depth of field is larger and the image can be focused widely, it is often used in the endoscope in which it is structurally difficult to construct the image capturing optical part having the focus adjustment mechanism for driving multiple-lens systems. As the endoscope often captures the image of the physical object existing at the short range between several millimeters to dozens of centimeters, the above-described barrel-shaped distortion occurs significantly.
In case of capturing the image by using such imaging apparatus as described above, there raised a requirement from the user in order to recognize the actual dimension of the physical object in the captured image displayed at the displaying part. In order to meet such requirement, there is such a proposed technology that a plural of image capturing means for capturing the image of the physical object are provided at the endoscope, calculates the three-dimensional coordinates of the representative points in a plural of captured images on the basis of the positional relationship of those representative points, and then displays the graded scale as an over layer onto the captured image on the basis of the calculated three-dimensional coordinates (for example, refer to JP 2002-156212 A).
There is also such a proposed technology that, in the endoscope, an endoscope position and direction detecting means for calculating the spatial position and direction of the top of the endoscope, a displacement information working-out means for calculating the displacement of the endoscope image along the direction in the plane based on the movement of the individual points in the successive endoscope images, and a depth information working-out means for calculating the three-dimensional coordinates of those points in the endoscope image on the basis of the spatial position and direction of the top of the endoscope and the displacement of the endoscope image along the direction in the plane are provided, and then the graded scale is displayed on the basis of the calculated three-dimensional coordinates of those points (for example, refer to JP 2000-210248 A).
There is also such a proposed technology that, in the endoscope, a measurement light scanning means is provided, and then the distances between the individual points on the scan line of the laser light and the top of the endoscope are calculated, and then the graded scale is displayed on the basis of the calculated result (for example, refer to JP 05-041901 A (1998)).
There is also such a proposed technology that, in the endoscope, a distance image sensor is provided for capturing the range image representing the two-dimensional distribution of the distance-to-object, and then the graded scale is displayed on the basis of the calculated result (for example, refer to JP 2005-087468 A).